Hello!
This is second lecture on introduction to Remote Sensing As you can see that now we
are going to discuss in this particular topic the development of Remote Sensing technology
and advantages So we will look some history and we will see that why Remote Sensing is
so useful that means the advantages There are various advantages of Remote Sensing over
conventional techniques and we will see all those details
As I mentioned in the previous lecture that is the introduction to Remote Sensing first
lecture that the current remote and sync is you know is not did not develop in just 1
day it took you know centuries basically as you can see that the first time the Ariel
photograph was taken from a hot air
Hot air balloon in 1858 as a drawing shown here and the photo luckily these been preserved
so the photographs of uh through that camera which we have taken are also shown here So
remote basically that was also remote sensing which brought us to this current day remote
sensing So it is basically if you look the history of remote sensing and the development
the journey the development journey of remote sensing basically we can put in 1858 and of
course a later on in World War 2 specially there are lot of extensive use of remote sensing
was done but before that also the you know that words were also used to put their the
cameras and then flown over it
So in 1903 this kind of experiment was done later on the plane mounted cameras were also
used in 1914 45 when this World War second was going on
And then in 1947 the first space based photo taken on 7th March 1947 and this photograph
is shown like this but these were not scanners these were not imaging system these were the
cameras and we took the snapshot there is a large difference between these snapshots
and scanning which we will see in later lectures So this this was taken by an automatic camera
K12 using black and white infrared film and from Viking sounding rocket that reached the
height of 227 kilometre
Nowadays these polar orbiting earth orbiting satellites are orbiting around 800 and plus
850 minus few kilometres they are orbiting so much deeper in space the current day remote
sensing is been done But anyway this is how things developed first through you know balloons
and then you know space ball or space based photo taken and this is a New Mexico Arizona
Nevada California and New West Mexico was captured in 1947
In a 1961 the earth this was taken by satellite which is Mercury-Redstone 3 spacecraft on
5th May 1961 and which was the first US man space flight so this was a man in this space
flight man was there and or astronaut was there and it has taken the photograph Later
on other in (alad) other missions also like Apollo Lunar landing missions also the photographs
not only of the earth were taken but also of the moon
The real remote sensing the boom in remote sensing really started since 1972 after the
first launch of this series of satellite and the first one in that series was Landsat Earlier
if you open some older books you would find that the name of this satellite was ERTS Earth
Resources Technology Satellite later on it was renamed as Landsat So we started the real
operational to the current remote sensing if since 1972 and the good part is that the
most of the data which this satellite the series of Landsat have recorded are not available
for us to use
So more than 45 years of now roughly 45 years of the data is available and therefore people
are implying this data sets for long term studies specially in climate change or in
environmental related studies So that is the biggest advantage that the archive since 1972
after the Landsat 1 which was launched on 23rd July are now available almost free of
cost for utilization for different applications
Then another boost came because the Landsat 1 was giving the data it has the sensor which
is the multi spectral scanner MSS and it has resolution of 79 or roughly say 80 metre Now
this was improved this special resolution was improved much much improved special resolution
through this spot which was a French orbiting satellite in 1986 and it had the new sensors
very high resolution relatively at that time very really high resolution that means it
started providing data at 10 metre that was the panchromatic that means black and white
and also 20 metre that is this multi spectral data though this spot so that brought a major
jump from special resolution from roughly 80 metre to 10 metre and 20 metre that was
a great boost to remote sensing though this program of French earth observation satellite
that is spot in 1986
Nowadays many many countries more than 12 countries are having their own satellites
including India including China Japan and a even you know Dubai which is UAE Dubai is
city of UAE which is a not a very big in that sense but they too are having their own satellite
so now many many countries are having satellite and that is why the earth is enveloped by
many many types of satellite many of them are working and some of them have lived their
lives or have become defunct and they are though they are present in space
So in 1970 80 the repeated ones in digital image processing parallel also developed and
that also basically brought impetus in the remote sensing technology because the data
started coming lot of data started coming from various satellite and the same time good
digital image processing tools specially software tools were developed so that people can utilise
analyse the data make good interpretation and excellent applications
In 1980’s the development of hyper spectral sensors like a Landsat MSS there were only
4 bands people started looking more thinner bands means narrow bands and also many bands
and that basically brought the development of hyper spectral sensors Earlier these sensors
where initially they were flown on aircraft tested and then later on they were on put
on the satellite like one of the example of Aviris which was developed by NASA and they
had many channels not 4 channels 10 channels or 36 channel like now days but they had like
200 channels 155 channels or 255 channel
So for for a very micro metre thick thick bands made available so there is another large
development which has taken place in remote sensing Now there are satellites also in a
(spec) hyper spectral range as well Then in 1990’s this global remote sensing system
started coming that means we had we developed better communications so we can cover any
part of the earth anytime and that kind of thing
If we look the development of remote sensing in India so it started basically in 1975 when
we had our first satellite launched that was named as Arya Bhatt and later on then we had
the Bhaskara 1 Bhaskara 2 and they had some cameras visible near near infrared camera
and also some micro wave radio metres also at that time Later on the the real as in case
of word remote sensing the Landsat became the landmark development
So in case of Indian remote sensing the IRS series became the landmark and basically it
started in 1988 in March 1988 the IRS 1A a satellite which was launched we will see go
through a list of a Indian satellites and foreign satellites how the in the history
we can put them and in a (chronical) chronological order that the IRS system is the largest constellation
of remote sensing satellite for civilian use of operation today in the world with a 12
operational satellite
So now we are left at series IRS 1A 1B 1C 1D after that then we are having Cartosat
source at very recently Cartosat 2 have also been launched and then this program of Indian
remote sensing program continues and even we are launching the satellites only roughly
3 years back we have also completed 25 years of our successful remote sensing operations
in a space
So they say this put the (pers) in perspective the landsat program as I mentioned earlier
that is started in 1972 1st July 1972 and it lived a quite long life about about 5 more
than 5 years though generally these uh type of satellites are designed for mainly 3 years
but they if design part is good launch is good then they may live even for 10 years
So this this was very successful mission than Landsat 2 came Landsat 3 came 4 5 6 was very
short lived satellite Somehow there were some technological problems and then 7 and 8 8
too has become very successful and this is for the future which we will see very soon
The other important thing is which you you should be able to notice is that there are
overlapping all the time that it is not that which every the country who which are having
long term remote sensing programs they always go for overlap and they say in Indian but
like we are looking the Landsat case that see this roughly in the half time another
satellite was launched so for a few years we had a 2 satellites together in tandem in
space of Landsat series then then when Landsat finished then Landsat 2 and 3 were there in
the space There were some less overlap was there then a very longer overlap and similarly
in case of our IRS series and other we also had this kind of overlap
So what what it provides that there is a continuity of the coverage by our own satellite or by
a particular series of satellites and secondly that the repeativity is a suppose a once the
the the repeativity or we call as a temporal resolution is revisit time Suppose a satellite
having revisit time of 16 days now if you are having 2 satellites in tandem really for
whatever the time period we are having and if they are designed or put in space in a
manner that a after every 8 days you will have 1 scene of 1 scene of the same part of
the earth So this is the advantage of having overlapping satellites in tandem
Here is this our ISRO mission and we have we are only looking uh after this IRS that
is March 1988 onward of earlier we were using as you might be knowing that some foreign
(sat) vehicles launching vehicles and but then the IRS 1D we started with our own PSLV
series of our launching vehicles and since then we have been not only launching our own
satellites but the foreign satellites of different countries even US Russia and France and many
other counties Satellites are now being launched by the launching vehicles which is PSLV
So IRS 1A and this series continued P P4 P5 P6 then Cartosat Cartosat 2 then Oceansat
Cartosat 2B and Resourcesat RISAT this is a different satellite this is radar remote
sensing satellite but that too have been launched in 2012 so many of them I are still in service
some have completed their missions and so on so forth This is because each satellite
has got some design life many of them lived more than designed life many because of some
other reasons may not live even their design life but that is very rare thing
Now this this thing between the remote sensing which is available to us through sensors means
imaging devices scanners and the other side of the data is available through Ariel way
so we will see the difference point by point that what is the basically the difference
between the normal remote sensing or Ariel photography which was a technology lasted
for many years was quite useful So what we see is that the current satellite remote sensing
is having very high speed high temporal resolutions like it depending on the special resolution
if it is having relatively coarser (ap) special resolution it can provide the data of the
same part of the earth even 2 times or 4 times in a day
For example NOAA AVHRR data in there are satellites which can provide data even after 35 days
like radar remote sensing data so depending on their orbits and the resolutions this thing
is there but for in case of Ariel photography it is slow it has to be you know put in it
has to go in the air and then take the photographs of a small part of the area whereas satellite
keep scanning different parts of the earth continuously day time and night time if they
are having thermal sensors so that is the biggest advantage
Say regular thing and we can say Ariel photography is not regular once the satellite is launched
and if it is is it becomes operational then regularly it is scanning the part of the earth
whereas it is not true in case of Ariel photograph and levels of details Nowadays like GUI satellite
we can have even 50 centimetre special resolution data which is may not be possible with this
sometimes with Ariel photographs will low flying air photographs we can have 2.5 centimetre
but this very very rare and very expensive as well
Weather conditions cloud is a big hindrance in optical data especially with the satellite
data so this is a sort of negative in case of present day remote sensing but in case
of Ariel photograph you can avoid if you know there are clouds the area which you are going
to cover you will not fly the aircraft so that can be avoided Then type of data the
less as each new data type needs new satellite launching so type of data is also available
wide variety of data is available from satellite whereas the type of data high as new data
types needs sensors to be mounted in aircraft
Location now there is another advantage the as I mentioned that the big impetus came remote
sensing in World War 2 so that the territory across the territory people will wanted to
have the information and therefore the at that time Ariel photography started and oblique
looking obliquely in other side across the border So location cross border images and
large swath images can easily be taken by the satellites which are doing regularly and
the location here cross border images cannot be taken without permission generally but
in case of war or some emergency situations these things are being done
Now post processing is required in case of satellite data which but because of huge development
in digital image processing and a very advance some semiautomatic or automatic image processing
tools are available which makes us to process large amount of data which is being acquired
by the satellite and then post processing it is tough though due to large number of
images covering a small area because the Ariel photograph these are having fixed size and
they becomes in very large number they are mosaicking they are processing becomes very
very difficult because they suffer from lot of distortion because of the movement of the
these Ariel photographs So this brings the basically the major differences between satellite
remote sensing and Ariel photography
Now this current day remote sensing can be divided in 2 major parts basically 1 is active
remote sensing and another one is passive remote sensing Passive remote sensing is very
popular active remote sensing is having limitations but now days it is becoming popular an especially
with the development of this SAR Interferometry and many many countries are not having their
own satellites or planning to have their satellites in active remote sensing but there are only
few satellites in space in this domain
Whereas the passive remote sensing is much easier and lot of satellites are there Even
in passive microwave regions they were some experiments were also done so passive provides
a lot of remote sensing data so that is because passive does not employ any external source
of energy and whereas in case of active remote sensing has it own source of energy What does
it mean Basically it means that because for passive remote sensing either you are having
solar radiation reflection reflective radiation which is available to the sensors which can
record the different objects of the earth especially in day time or a emitted energy
can also be recorded maybe in micro wave region as well
So for that you don’t require any external source of energy whereas here in case of active
remote sensing the satellite of the sensor itself has to send some signals energy and
then that is a attenuated reflected back and then collected later so that is why it is
less common but it is becoming very powerful tool of remote sensing that is active remote
sensing especially SAT Interferometry which we will see little later
Now the passive what passive remote sensing is doing as mentioned earlier the measures
either reflected radiation from the sun can be operated only during day time or the emitted
radiation from the surface day and night time so if you are having thermal sensors you can
record the data even in night time like in case of Landsat after Landsat 4 till Landsat
8 all these are having thermal sensors and therefore even in night time you can record
the emitted energy through these thermal channels same with the NOAA AVHRR data
So no AVHRR sensor on board of this NOAA satellites are also having 2 channels in thermal thermal
band and therefore we can also record the data in night time as well Though they are
also having visible and near infrared and infrared channels as well so that is the advantage
of having this kind of passive remote sensing Active sensors emit a control beam of energy
to the surface of the earth and then whatever is reflected back it is recorded and this
is how these images of microwave basically microwave remote sensing images are formed
Then passive remote sensing so first from variable illumination conditions of the sun
because you know that the sun having the you know varied illuminations depending on
the season because of clouds and so on So that might create some problem in our passive
remote sensing and may influence the atmospheric conditions as well that we have also discussed
little earlier we will see in much detail what are the atmospheric distortions and how
these quickly can be corrected in some cases
And here what we are having because the satellite or sensor itself is sending the energy and
therefore it is controlled illumination signal so that question of atmosphere and other things
will not come because here the wavelength is larger and then that atmosphere present
between sensor and the earth does not create much problem here These operations in active
remote sensing can be done day time or night time there is hardly any difference because
the the source of energy from satellite itself sensor itself
Then what are the advantages this is this is the B point basically which brings the
usage of remote sensing or why it has become very popular in the last 30 40 years First
of all it is it provides the synoptic view what does it mean synoptic view means here
that in a in a when it is satellite is orbiting it may cover a very large part of the earth
and another very important thing which that point might come later in the slides is that
it records the unbiased in a unbiased manner so whatever the recording which is available
there is no human interventions directly the sensors is recording so it provides a unbiased
recording and a synoptic view
A large part is covered by these and another advantage it is a global coverage most of
the satellites these satellites are covering entire globe though somebody might not be
recording that the data or somebody may not be having the earth stations in different
counties of all satellites but the satellite itself might be transmitting the data or directly
broadcasting the data towards that and covering the different parts of the or all parts of
the earth so that is another very good advantage with remote sensing global covering
Repeatability it keeps covering same part of the earth depending on the resolution and
the orbit so some satellite as I mentioned that like NOAA AVHRR sensor they can cover
even 4 times in a day 2 times in day time 2 times in night time whereas some satellites
may come after 12 days 16 days 18 day depending on the their resolution swath width and so
other things
Now multi multi spectral sensors can another advantage with remote sensing that not only
you are recording in panchromatic but you are also doing a multi spectral sensor so
can that can also be that can be recorded wavelength beyond range of human reason as
mentioned in the the first lecture that our eyes are only sensitive in visible part of
the earth whereas the sensors we can design which can sense the earth or scan the earth
not only in visible part but near infrared infrared thermal infrared even in passive
microwave regions so multi spectral sensors are available through remote sensing which
is otherwise not possible
Multi resolutions data even on 1 same satellite we can have different sensors having different
resolutions example came about spot so it has panchromatic camera 10 metre resolution
it has 20 metre resolution multi spectral data same example started coming with our
own IRS satellites we had once a this (pan) panchromatic camera at 5.8 metre resolution
and then we had the les 3 sensors like 23.5 metre resolution so same satellite can have
different sensors of different resolutions so that is another advantage for the same
day you are having different resolution data from the same satellite so that the atmospheric
conditions are constant throughout these sensors
Near real time it is possible when because when the satellite is over passing generally
these are also directly broadcasting or transmitting data towards that If a these data is not
incorrupted one can even have their own satellite earth station like an IIT Roorkee department
of earth science since 2002 we are operating NOAA AVHRR earth station because NOAA is directly
broadcasting so we don’t have to have a license or encrypting code or any other thing
we can just record the data whenever the satellite is over passing our earth station
So in near real time the data is coming there is another advantage especially in disaster
related applications that provides the very big advantage systematic data collection because
these the orbits are fixed when the satellite will come we know in advance even 7 days 8
days before we know then when satellite will overpassing a particular part of the earth
so lot of things can be designed accordingly lot of missions can be designed and therefore
the data collection is very systematic through remote sensing and this is the only solution
sometimes for otherwise inaccessible areas
Especially like in high mountain terrains like Himalaya where highly rugged all parts
cannot be reached very easily by the humans or by other means but remote sensing can reach
so that is the very big advantage Same thing also happens in case of any natural or manmade
disasters that the first thing people start looking remote sensing because it can acquire
the data there might be some satellite at that time might be flying over of that part
of the earth where a natural disaster has occurred and therefore you can get the data
and analyse and can see how things developed or this has happened
And I have a very important point which I mentioned about these 3 technologies that
is remote sensing GIS and GPS that these are the generic technologies and therefore their
applications are you know many several and some still we don’t know people are developing
so the generic the remote sensing data is generic and therefore it has got multipurpose
application so it can be applied for various things from climate change to natural disaster
to civil engineering to mineral exploration to Isle exploration whatever where ever one
can think can now a days can apply
Metrological applications are there and therefore weather forecasting it is now extensively
being used this technologies in integrated manner And of course it is cost effective
because once the satellite is launched it may last may live for 5 years 6 years sometimes
they live for even 10 years and keep providing data continuously and therefore the initial
cost is much more and later on only the some operational cost recording of the data making
archive and of course analysis interpretations those things are there but even then overall
of you see it is highly cost effective technology compared to other conventional methods and
specially ground surveys and other things
So this brings this in a large perspective we can see that the remote sensing is unobtrusive
if the sensor passively record the EMR that is the Electro Magnetic Radiation Reflected
or emitted by the object of interest passive remote sensing does not disturb the object
or area of interest So whatever is being done it untouched by any sensor and the remote
sensing devices may be programmed to collect data systematically such as within a 10 kilometre
by 10 kilometre frame or vertically photography this systematic data can collection can remove
the sampling bias introduce in some of the because this term I have used the remote sensing
provides completely unbiased recordings of the any any event which is happening on the
earth anything which is happening on the earth
For example there might be forest fire for example there might be earthquake and ground
(defo) associated ground deformation and might be flooding so on and so forth so this is
completely unbiased recording is also available Under control condition remote (cansing) remote
sensing can provide fundamental biophysical information including location elevation daft
biomass temperature moisture content because if we integrate the GPS then we get the location
If we integrate or put on GIS platform we can expect few more things that temperature
is being driven from remote sensing through this thermal sensors and there are different
algorithms by which we can estimate the temperature of the earth or even sea surface temperature
or a temperature over a volcano temperature over a forest fire or coal fire coal mine
fire those things can also be done and of course moisture content and other thing people
have developed application not only in this infrared or other parts but also in microwave
remote sensing So this brings to the end of this second lecture on introduction to remote
sensing Thank you very much